1. Field of the Invention
The invention pertains generally to electromagnetic coil apparatus and, more particularly, to solenoid coils for an electrical switching apparatus accessory. The invention also pertains to electrical switching apparatus accessories, such as, for example, shunt trip and under voltage release modules. The invention further pertains to electrical switching apparatus, such as, for example, circuit breakers.
2. Background Information
Electrical switching apparatus, such as circuit breakers, as well as transfer switches, network protectors and the like, are often equipped with accessories such as, for example and without limitation, shunt trip devices and under voltage release (UVR) devices. Such devices can be employed in a variety of ways to initiate a change in status of the apparatus such as, for example, to trip open the separable contacts of the apparatus in response to an electrical fault condition (e.g., without limitation, current overload; short circuit; abnormal voltage) or other external condition.
In view of the increasing market trend to reduce the overall size of the circuit breaker, the space which is available within the circuit breaker housing is limited.
Referring to FIG. 1, typically, a shunt trip device 2 (or UVR device (not shown)) includes a number of coils 4, a frame 6, a plunger 8 and a heel 10, which cooperate to form a substantially closed magnetic circuit. A plunger stem 9 is further extended (not shown) in response to movement of the plunger 8 to, for example, engage and pivot a trip bar (not shown) to cause a circuit breaker (not shown) to trip open separable contacts (not shown). When one of the two example coils 4 is energized with a sufficient voltage, magnetic flux 12 is transferred through the ferrous parts of the magnetic circuit. As shown in FIG. 1, a south (S) magnetic pole is generated at the heel 10 and a north (N) magnetic pole is generated at the plunger 8. This attracts the plunger 8 to the heel 10 and causes the plunger to move.
It is desirable to maximize plunger force, in order to ensure an effective and reliable trip mechanism. Some of the known and typical ways to maximize plunger force include increasing the diameter of the plunger, increasing the number of windings in the coil(s), and increasing the amount of magnetic flux transferred to the plunger. However, the size constraints of the coil(s) (e.g., the outer diameter thereof) in a circuit breaker may make it impractical to either increase the diameter of the plunger or to increase the number of windings in the coil(s), both of which would tend to increase the outside diameter of the coil(s).
U.S. Pat. No. 6,377,146 discloses an electromagnetic relay with an electromagnet operatively associated to a ball actuator in order to drive a control rod. The electromagnetic relay is housed in a recess of a case and includes an internal shunt designed to enhance the magnetic field, a magnetizing coil that substantially surrounds the internal shunt and a portion of the control rod, a stopper enabling the magnetic flux to be reclosed, and a return spring. The control rod is made of ferromagnetic material and, thus, constitutes a plunger core biased by the return spring in the enlargement direction of the air-gap between the control rod and the internal shunt.
There is room for improvement in electromagnetic coil apparatus.
There is also room for improvement in electrical switching apparatus accessories.
There is further room for improvement in electrical switching apparatus, such as circuit breakers including accessories.